The invention relates to a getter pump, in particular for use inside the vacuum chamber of a vacuum coating installation, as well as a vacuum coating installation having a getter pump of this type.
A getter is a chemically reactive material which is used for the purpose of maintaining a vacuum as long as possible or also generating a vacuum. Gas molecules form a compound with the atoms of the getter material on the surface of a getter. Gas molecules are captured in this way. This principle is used, for example, for binding residual gases remaining in the vacuum. The gas precipitates on fresh, uncovered surfaces. If the layer is formed by vapor deposition of a metal, one refers to getter pumps. Titanium is usually used in the getter pumps of vacuum technology. Platinum is also suitable.
In vacuum coating installations for the deposition of alternating layer systems made of chemical compounds, often oxides, and metals and simultaneous layer deposition, a very effective gas separation of the processing gas atmospheres of the various coating processes is necessary. If this separation, which is often referred to as gas separation, is not provided, there is a clear degradation of the properties of the metal layers.
Typical applications are the production of highly reflective mirrors, the vapor deposition of alternating layer systems made of oxidic, nitridic, and metallic layers for implementing heat protection functions, and the production of cermet layers. Cermets (from the English words ceramic and metal) are composite materials made of ceramic materials in a metallic matrix (binder). They are distinguished by an especially high hardness and wear resistance.
Gas separation units typically comprise a combination of flow resistances and pumps. For higher demands on the degree of separation, differentially pumped separation stages are used. Turbo-molecular pumps or diffusion pumps are typically used.
Geometric limits also apply from a technical aspect for the flow resistances, so that the individual conductances may not be set arbitrarily small. A higher degree of separation thus requires a very high suction performance for the reactive processing gases. Geometric limitations also result here on the one hand, and cost limitations result on the other hand.
So-called getter pumps are a very effective type for suctioning reactive gases. Metal electrodes are atomized in a glow discharge process. The freshly deposited metal layers adsorb, i.e., getter, incident reactive gas particles and thus act as the pump. Because new material is continuously atomized, this process may be continuously maintained. In the limiting case, getter pumps may achieve an area-related suction performance which corresponds to the conductance of a screen opening in the molecular flow range. However, this is only true if the getter surface faces directly toward the gas flow.
In conventionally constructed systems, however, this is not the case. The reason for this is that the substrates to be coated are typically to be protected before the vapor deposition of the metal vapor used for the sorption. Examples of systems of this type are the devices known from JP 2001/234326 and U.S. Pat. No. 5,980,213. A disadvantage of conventional apparatuses is the only indirect access of the reactive gas to the getter surfaces, which limits the efficiency of such an apparatus.
A device is known from JP 7138739, in which a coating chamber 1 and a vaporization chamber 2 are connected to one another by a valve 8. The substrate 5 to be coated is situated in the coating chamber 1. The vaporization chamber 2 is divided by a screen 10 into two partial chambers connected to one another. A first vapor source 3 for coating the substrate 5 is situated in one partial chamber and a second vapor source 4 for vaporizing the getter material is situated in the other partial chamber. It is not possible to prevent getter material from precipitating on the substrate in this device.
To solve this problem, it is suggested in JP 5001664 that a getter pump 4 having a getter pump housing 5 be situated on an opening of the wall 13 of a vacuum chamber 1 in such a way that a rotor 6 partially projects into the getter pump housing 5 and partially into the vacuum chamber 1. A titanium sphere 8, which is gradually atomized, is situated in the getter pump housing 5. The getter material atomized from the titanium sphere 8 precipitates on the rotor 6, i.e., the rotor 6 is solely used as a carrier for the getter material. By the rotation of the rotor 6, the layer of getter material deposited thereon is moved into the vacuum chamber 1. A disadvantage of this solution is that the rotor 6 must be replaced after a certain operating time, because the deposited layer becomes thicker and thicker. Shutdown times, which cause costs, arise in this way. In addition, the danger exists that getter material will penetrate between the rotor 6 and the opening of the wall 13 of the vacuum chamber 1 into the vacuum chamber 1 and contaminate the substrate in this way, because the material atomized from the titanium sphere 8 is emitted in this direction.